1. Field of the Invention
The present invention relates to a tungsten heavy alloy, and in particular, to a fabrication method for a poreless tungsten heavy alloy containing manganese.
2. Description of the Conventional Art
Conventionally, a tungsten heavy alloy is composed of more than 90 weight % tungsten, nickel(Ni), iron(Fe), cobalt(Co) and manganese.
When manganese is added to a W--Ni--Fe type tungsten heavy alloy or a W--Ni--Co tungsten heavy alloy which is chiefly used as a material for a penetrant of a kinetic energy penetrator, the manganese micronizes tungsten particles, and promotes an adiabatic shear band.(A. Bose, H. Couque, J. Lankford, Jr., "Influence of Microstructure on Shear Localization in Tungsten Heavy alloys," MPIF Princeton, N.J., 1992, pp 291-298.) By micronizing tungsten particles and promoting an adiabatic shear band, the mechanical properties and the energy-concentrating degree of a tungsten heavy alloy are increased which consequently contributes to an improvement in the penetrating force.
Therefore, to improve the penetrating force of a kinetic energy penetrator, a W--Ni--Fe--Mn type heavy alloy and a W--Ni--Co--Mn heavy alloy have been developed recently by adding a small amount of manganese to a W--Ni--Fe type heavy alloy and a W--N--Co heavy alloy.
The W--Ni--Fe--Mn type heavy alloy and the W--Ni--Co--Mn heavy alloy are fabricated by liquid phase sintering as follows; First, a proper composition of powders of tungsten, nickel, iron, cobalt and manganese are mixed and compacted, and then a liquid phase sintering is performed under a hydrogen atmosphere, as shown in FIG. 1.
FIGS. 2A and 2B are photographs of fine grains of a W--Ni--Fe--Mn tungsten heavy alloy according to the conventional art observed through an optical miscroscope. As shown in FIG. 2A, when 0.1% manganese is contained, round tungsten particles are uniformly distributed in the matrix phase.
However, as shown in FIG. 2B, when more than 0.5% manganese is contained, black pores are disadvantageously formed.
The formation of such a black residual limits the content of manganese, and lowers the mechanical strength of the heavy alloy significantly, and consequently limits the use of the tungsten heavy alloy as a material for a penetrant of a kinetic energy penetrator.
Therefore, to use a tungsten heavy alloy containing manganese for a kinetic energy penetrator, the formation of residual pores should be controlled and the content of manganese should be increased.